Fire Cement

[Chris Learmouth]

I have installed a wood/coal burning cast iron insert and mantlepiec

and have filled the space behind the insert with hardcore. I have bee told, in the interest of safety, to skim the top of the hardcore wit fireproof cement. All I can find is 2kg tubs of fire cement fro Wickes which I have used to do some repointing inside the fireplace Although relatively inexpensive, I would need quite a few tubs to put screed over the hardcore. Is there a fireproof cement that can b bought in larger quantities or is there something I can add to norma cement? If not can I render with a sharp sand/cement mix then skim ove with the Wickes fire cement? I have visited most of the builder merchants and fireplace suppliers in Bedford but have been greeted wit blank expressions. Any advice would be greatly appreciated

-- Chris Learmouth

[The3rd Earl Of Derby]

You only need it around the inside edge of the fireplace,hence why they only sell it in small 2Kg tubs

[Andy Dingley]

Talk to Purimachos in Bristol. Helpful and cheap, if you're avoiding the retail layer.

Usually the face is a solid slab that you buy ready-made, the infill is vermiculite and you only need a small tub of fire cement to fill the gaps. There are also DIY recipes (concrete, but with vermiculite as aggregate) if you need to cast something monstrous.

[.]

the two I've done have remained uncracked for 8 and 4 years respectively.

[Chris Bacon]

It sounds as though he's got a cast-iron insert with no fireback, rubble-filled behind in the normal way.

[Chris Bacon]

You must be lucky, then, it's cartainly not recommended. What mix did you use?

[.]

can't remember. 2:1 ? 3:1 OPC & building sand. there may be microcracks in the flaunching but it all gets sooted up quite quickly. I also used a slurry of vermiculite & cement to backfill the firebacks.

[calums]

Chris The rubble infill is purely to disperse heat away from the cast iron fireplace. This help to protect the cast iron and prevent possible cracking. The screed is not too critical to the performance (IMHO) but will help to prevent moisture ingress, and also soot falling behind the insert when the chimney is swept. I would go for a weak sand cement mix, and if you wanted to be particularly fussy then some lime might be a good idea. Calum Sabey NewArk Traditional Kitchens (01556 690544)

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Chris Learmouth saying something like:

From another place. How to make fire cement...

A good heat insulation material can be made either from mica or pearlite.

Expanded mica granuls are sold as a soil adiditve to keep the soil free drained, as isulation as is pearlite which is white beads of mineral. Expanded mica is a better insilator whilst pearlite probably has the advantage of highte compressive strength and may incandess better than mica.

You can make any shape you with from either material by mixing enough water with the matereial to make it damp but NOT WET. You can then dust the damp mix with 'high alumina' cement, then when throroughly coated pack into moulds of the correct shape. You must not use ordinary cement as it will not stand the heat.

Alternativly you can use sodium silicate, or commonly it used to be called 'water glass'. You mix the sodium silicate with water and then use it to mix in with your agregate (the insulation). It sets to a glass like material to bind the insulation together. The one problem is with it is that it takes time to set, the two advantages are that it does not alter the reflective qualities of the agregate by coating it with a grey or black cement, instead it is galss clear so the mica chips or the white pearlite still reflect heat and the gloss surface adds to this. At very high temperatures the glass softens so becomes a little plastic. The great advantage is that the 'stock' of sodium silicate not used will last for donkey's years where the cement will go off and probably have to be purchased in 20kg bags.

Sodium silicate sets by absorbing carbon dioxide either from the air as it dries or by blowing carbon dioxide through the material. Placing the moulded material after sufficient drying to get it to hold up, in a carbon dioxide rich poly bag etc will speed up the curing.

Using methods like this you can make and re-make refractory and insulation materials from broken fire bricks. fired expanded clay pebbles and all sorts to suit your needs.